Available gaze tracking equipment may at times suffer from poor accuracy, mainly due to poor head movement compensation in the gaze tracking algorithms. Since the head generally moves slowly compared to the eyes the poor accuracy can, as seen over a short period of time, take the form of a constant error term (error vector) in the measured gaze point. Calibration of such systems may prove problematic insofar as a series of measurements may be needed, wherein each calibration (e.g., a nine-point or twelve-point measurement) corresponds to a particular head position and may be relied upon whenever the user's head is in or near this position in the future. A calibration procedure with a series of measurements will be experienced as complex by many users and is prone to human errors.
Quite often, however, such gaze tracking equipment is in fact able to measure relative motion vectors with good accuracy as the constant error terms referred to above may be expected to cancel. This is one of the assumptions underlying gaze-based moving GUIs, in which a user submits a command to a computer system by following a motion path of a graphical control on a visual display rather than fixating a stationary locus of the graphical control. For instance, the computer system may be configured to interpret a user's gazing at a moving graphical control as an intentional input operation if it has proceeded for more than a predetermined minimum time period. As used herein, an “input operation” is to be understood broadly, encompassing all of view-controlling commands (e.g., a scroll operation), system commands (e.g., launching an application) and entry of new content (e.g., typing text in an application).
In addition to the visually distracting movements of the graphical controls, gaze-based moving GUIs share a certain disadvantage with gaze-based GUIs in general, namely, that the user's fear of making an inadvertent input just by looking at an object (for too long) may build up some discomfort associated with the GUI. Whether based on this insight or other factors, some developers of available gaze-based moving GUIs have provided these with a functionality of temporarily disabling the moving controls.
U.S. Pat. No. 6,243,076 discloses a purely gaze-actuated GUI, which intermittently displays moving visual targets that the user may fixate to make an input to the system. The moving visual targets move along fixed, repeating, preferably pre-calculated paths or along random paths. The applications executing on the system may query the user for input by placing the visual targets in motion and removing them from the display image when the application is satisfied with the input received so far. Alternatively, the user invokes one or more moving visual targets. The behaviour of the visual targets is similar to that of conventional dialogue boxes, except that the user may not dismiss the visual targets voluntarily. As such, whether the interface is to be in an input mode (with moving visual targets) or a non-input mode (with stationary visual targets) is left at the discretion of the application, so that each developer will be facing the task of balancing two conflicting interests as far as the user is concerned. Indeed, the interest of a high responsiveness and controllability requires a high propensity for the application to enter the input mode, while the goal of promoting a peaceful working environment would seem to advocate infrequent use of the input mode and returning to the non-input mode as soon as possible.
US20110169730 and U.S. Pat. No. 8,235,529 disclose further purely gaze-actuated GUIs. By fixating a predefined display area, a user of the GUI according to US20110169730 may trigger an input mode in which one or more icons move linearly over a portion of the display, and the GUI will activate a predetermined functionality in an associated personal computer system when it detects that a user is pursuing an icon. The motion of the one or more icons continues until the GUI notes that the user is not pursuing any of them. As stated, the GUI enters the input mode as a result of deliberate fixation of a certain activation area, which in the implementation translates into detecting a dwell time above some predetermined threshold time. Because the activation takes place in the error-sensitive mode, in which the GUI detects location rather than movement, the activation area should be chosen sufficiently large. Further, the GUI should be robust against inadvertent activation of the input mode—it may take several input steps to leave the input mode if it is entered by mistake—which speaks in favour of a long threshold time for activation. This however runs counter to the goal of providing an agile and convenient GUI.
It may be said that neither of these known GUIs meets the expectations of demanding users. At the very least, their inconveniences are so significant that most users, who are in a position to freely decide whether to use a gaze-based human-machine interface or a conventional interface with a hand-actuated pointing device, are likely to opt for the conventional interface.